1. Field of Invention
The present invention relates to welded steel products having remarkably lowered sensitivity to weld cracking and a production method thereof.
2. Description of Prior Art
In welding of steel structurals, weld cracking (cold cracking or delayed cracking) has been one of the most serious problems.
Weld cracking occurs in metal of the weld, heat affected zones and sometimes base metals near the affected zones, either at temperatures below 150.degree. C when the process of cooling is coming to an end or during a long period after attaining the ordinary temperatures.
As for the means to prevent such weld cracking various welding methods have been proposed and practised, such as use of low-hydrogen welding rods, modification of welding designs to lower restraint of the weld joints and application of preheating and postheating. However, such heating procedure has been a troublesome operation for welding operators.
Meanwhile, from the aspect of the steel materials, various trials have been made for lowering the sensitivity of the steel materials to the weld cracking such as by lowering contents of harmful alloying elements which cause or promote the weld cracking.
However, the harmful elements which cause the weld cracking are generally necessary for enhancing the steel strength and hardenability, and thus in case of a steel having a high tensile strength from 50 to 80 kg/mm.sup.2, the lowering of the alloying elements is limited.